Currently, the diagnosis and assessment of dry eye is hindered by tests that have poor repeatability, some of which cause discomfort due to their invasiveness. As a result most clinical studies involving dry eye treatment rely on symptomatic improvements as a primary outcome measure. However, symptomatic improvements are a poor measure in determining treatment effectiveness because with disease progression, the eye becomes desensitized from nerve damage. Also, it is common for patients to feel a reduction of discomfort of the eye before objective improvements can be noted by the clinician. An assessment based on symptoms alone is therefore inappropriate.13